The present invention relates to a process for coating detergent granules in a fluidized bed.
Recently, there has been considerable interest within the detergent industry for laundry detergents which have the convenience, aesthetics and solubility of liquid laundry detergent products, but retain the cleaning performance and cost of granular detergent products. The problems, however, associated with past granular detergent compositions with regard to aesthetics, solubility and user convenience are formidable. Such problems have been exacerbated by the advent of xe2x80x9ccompactxe2x80x9d or low dosage granular detergent products which typically do not dissolve in washing solutions as well as their liquid laundry detergent counterparts. These low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers prior to use, but less convenient upon dispensing into the washing machine as compared to liquid laundry detergent which can be simply poured directly from the bottle as opposed to xe2x80x9cscoopedxe2x80x9d from the box and then dispensed into the washing solution.
Granular detergent products are typically produced from one of two manufacturing methods. The first involves the spray-drying of a aqueous detergent slurry in a spray drying tower to produce detergent granules while the second involves dry mixing various components after which they are agglomerated with a binder such as surfactant. The resultant detergent particles are then dried to achieve an acceptable moisture content such that the finished product is flowable and non-caking in the package once delivered to the consumer. In both processes, the factors which impact these flow characteristics include chemical composition and type and length in the drying process.
Many surfactant materials included in granular detergents, including linear alkyl benzene sulfonates (xe2x80x9cLASxe2x80x9d), ethoxylated alkyl sulfates and nonionic surfactants, tend to be relatively xe2x80x9cstickyxe2x80x9d in nature, difficult to fully dry and lead to lumping, caking and flowability problems in the finished product.
Accordingly, the need remains for a process which can produce a detergent granule having improved flow properties and aesthetics and which may be included in detergent compositions.
This need is met by the present invention wherein a process for coating a detergent granule is provided. The coated granules have improved surface, appearance and flow properties. The coated granules of the present invention have improved surface properties in that they are smoother and have a generally more uniform surface and appearance than prior art detergent particles. Further, the appearance of the particles have been improved in that they appear brighter and whiter than currently available detergent particles and have improved flow properties where the particles have reduced lumping and caking profiles.
In accordance with the present invention, a process for coating detergent granules in a fluidized bed is provided. The detergent granules of the present invention are preferably selected from spray-dried granules, wet agglomerates, dry agglomerates, detergent adjuncts or mixtures thereof. Particularly preferred are mixed agglomerates which are agglomerated mixtures of dry agglomerates and spray-dried granules. The coating material may be selected from anionic surfactants, silicates, hydrotropes and non-hydrating inorganic materials. Particularly preferred are non-hydratable inorganic coating materials including double salt combinations of alkali metal carbonates and sulfates. The coating material may also include detergent adjunct ingredients such as brighteners, chelants, nonionic surfactants, co-builders, etc.
The fluidized bed of the present invention is operated at a flux number of at least about 3.5, and more preferably from about 3.5 to 7.0 and most preferably from about 3.5 to about 5.0. In addition, the fluidized bed is operated at a Stokes number of greater than about 1.
Accordingly, it is an object of the present invention to provide a process for coating a detergent granule. It is an additional aspect of the present invention to provide a process for producing detergent granules that have improved appearance and flow characteristics. These and other objects features and advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description and the appended claims.